1. Field of the Invention
The present invention relates to what is called a FIMS (Front-Opening Interface Mechanical Standard) system or load port apparatus that is used when wafers stored in the interior of a transfer container called a pod are transported between semiconductor processing apparatuses in a semiconductor manufacturing process etc. More specifically, the present invention relates to a load port apparatus in which the degree of cleanliness in what is called a mini-environment provided in the interior of the load port apparatus is improved as compared to conventional apparatuses, or a high degree of cleanliness can be maintained reliably, and to a dust exhaust method for removing dust from the interior of the load port apparatus.
2. Description of the Related Art
Previously, the semiconductor manufacturing process had been performed in what is called a clean room that is constructed by establishing a high degree of cleanliness in a room in which semiconductor wafers are handled. In recent years, however, to cope with an increase in the wafer size and with a view to reduce cost incurred in maintenance of the clean room, such systems have been reconsidered. In consequence, in recent years, use has been generally made of a method of keeping clean only the interior of each processing apparatus, a pod and a mini-environment through which substrates or wafers are transferred between the pod and each processing apparatus, thereby controlling the cleanliness throughout the process.
The pod is composed of a body in which wafers are stored and that has an opening provided on one side thereof through which wafers can be brought into/out of it, and a lid for closing the opening to seal the interior space of the pod. The mini environment has a first opening portion that can be opposed to the opening of the pod, and a second opening portion provided on the processing apparatus side opposite to the first opening portion. The load port apparatus includes a member or wall that constitutes a partition on which the first opening portion is provided, a door that closes the first opening portion, a door driving mechanism that control the motion of the door, and a support table on which the pod is to be placed.
The support table can support the pod in such a way that the opening of the pod and the first opening portion are opposed to each other. The support table is adapted to move the lid toward and away from the door together with the pod. The door can be caused by the door driving mechanism to hold the lid of the pod. The door is retracted downwardly away from the space between the first opening portion and the second opening portion while holding the lid. A robot is provided in the mini-environment. The robot has a part that can move into and away from the interior of the pod through the first opening portion and the opening of the pod and transfer wafers between the interior of the pod and the semiconductor processing apparatus through the pod opening, the first and second opening portions.
Normally, when the interior space of the pod in which wafers are stored is filled with a gas such as dry nitrogen having a controlled high degree of cleanliness to prevent contaminant and oxidizing gases etc. from entering the interior of the pod. However, when the lid of the pod is removed to allow the wafers in the pod to be taken out, the interior space of the pod and the aforementioned mini-environment is brought into communication with each other. To prevent the interior space of the pod from being contaminated through the mini-environment, a fan and filter are provided in the upper portion of the mini-environment. With the fan and filter, clean air controlled with respect to dust and particles is introduced into the mini-environment, thereby controlling contamination of the interior of the pod with dust etc. as much as possible.
The introduction of the external air into the mini-environment through the fan provided in the upper portion of the mini-environment creates down flow directed from the upper portion to the lower portion thereof in the mini environment. The down flow is intended to prevent dust, particles and the like generated by various driving mechanisms disposed in the lower portion of the mini-environment from adhering to wafers transported in the upper portion of the mini-environment and from entering the interior of the pod.
In the load port apparatus, when driving the door, various parts of the door driving mechanism that drives the door perform sliding operations. It is desired that dust generated by such operations be kept out of the mini-environment as much as possible. For this reason, the main drive system is disposed in a housing space for the drive system provided outside the mini-environment as described in Japanese Patent No. 3983219. The housing space and the mini-environment are in communication with each other through an elongated hole or the like having a minimum size. The driving mechanism supports the door through the elongated hole and operates the door in the mini-environment. In some cases, as disclosed in Japanese Patent Application Laid-Open No. 2005-167284, a forced exhaust apparatus such as a fan is provided in the lower portion of the housing space to forcibly discharge dust generated in the housing space to the exterior, thereby preventing dust from entering the mini-environment.
With increases in the packing density and improvements in the performance of semiconductor devices in recent years, the wiring width and the inter-wire gap have been made smaller. In consequence, it has become necessary to take care of smaller size dust particles that did not matter before. Dust can cause a problem in the semiconductor manufacturing process. The behavior of such very small dust particles is greatly different from that of the particles that have been conventionally taken care of. For example, very small dust particles are little affected by the gravity. For this reason, even if forced discharge is performed for the housing space using a fan as described in Japanese Patent No. 3983219, what is expelled effectively may be only the gas in the region near the fan and small particles floating therein.
In addition, the range over which the gas suction force of the fan acts is not so large. Therefore, it is considered difficult for the fan to exercise a significant influence on the direction of floating of minute dust particles at positions distant from the fan. Furthermore, in order to maintain the cleanliness in the mini-environment and to stabilize the motion of the gas in the mini-environment during opening/closing of the door, it is necessary that the pressure in the mini-environment be kept to be a little higher than the pressure in the external space. Therefore, it is practically not allowed to increase the efficiency of discharging minute dust particles by enhancing the performance of the fan, because the enhancement of the performance of the fan makes it difficult to maintain the pressure. In view of the above, there is a demand for a structure or method that can effectively remove minute dust particles or the like that are generated by the door driving mechanism and tend to stay in the space for a very long time.